Abstract

Withasteroids are a group of naturally occurring C28-steroidal lactones built on an intact or rearranged ergostane framework. Withaferin A (64), the first member of this group of compounds, was isolated (1) from the well-known Indian medicinal plant, Withania somnifera (Sanskrit: Aswagandha) and its structure was fully elucidated by Lavie and coworkers in 1965 (2). The structural novelty and interesting biological activities (3) elicited by this compound led to a thorough chemical investigation of the plant and numerous compounds having similar structural features were isolated. These C28-steroidal lactones characterised by a nine carbon side chain with a six membered ring lactone were designated as ‘withanolides’after the name of the plant genus (4). The withanolide skeleton may therefore, be defined as 22-hydroxyergostan-26-oic acid 26,22-lactone (I) and using this trivial name, withaferin A (64) may be designated as 4β, 27-dihydroxy-5β, 6β-epoxy-l-oxowitha-2,24-dienolide, the nomenclature that has been most widely adopted. However, many structurally related C28-steroidal lactones which do not conform to the above definition have also been referred to as with-anolides (5), a practice giving rise to confusion. Also, there are many novel structural variants of withanolides with modifications either of the carbocyclic skeleton or of the side chain and these have often been described as modified withanolides or ergostane-type steroids related to withanolides.

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